This invention relates to catalyst system for polymerization of monomer having at least one Ziegler-Natta polymerizable bond. It is notably effective with ethylene and other xcex1-olefins. Particular catalyst systems of this invention will comprise supported Ziegler-Natta catalyst which has been modified with metallocene-type or single-site catalyst, preferably during synthesis.
Polyolefin manufacturing processes typically involve the polymerization of olefin monomer with an organometallic catalyst of the Ziegler-Natta type. Catalyst systems for the polymerization of olefins are well known in the art. Typically, these systems include a Ziegler-Natta type polymerization catalyst component and a co-catalyst, usually an organoaluminum compound.
U.S. Pat. No. 4,530,914 discloses use of a catalyst system comprising two or more metallocenes in the polymerization of xcex1-olefins, primarily ethylene, to obtain a broad molecular weight distribution. The metallocenes each have different propagation and termination rate constants. Such metallocenes are mixed with an alumoxane to form the active catalyst system.
U.S. Pat. No. 4,701,432 describes a support treated with at least one metallocene and at least one non-metallocene transition metal compound. To form a catalyst system a cocatalyst comprising an alumoxane and an organometallic compound of Group IA, IIA, IIB, and IIIA is added to the supported metallocene/non-metallocene. The support is a porous solid such as talc or inorganic oxides or resinous materials, preferably an inorganic oxide, such as silica, alumina, silica-alumina, magnesia, titania, or zirconia in finely divided form. By depositing the soluble metallocene on the support material it is converted to a heterogeneous supported catalyst. The transition metal compound, such as TiCl4, is contacted with the support material prior to, after, simultaneously with, or separately from contacting the metallocene with the support.
It is known that Cp2TiCl2 in the presence of alkylaluminum compounds polymerizes ethylene but not propylene whereas in the presence of methylalumoxane (MAO), Cp2TiCl2 polymerizes propylene also to produce atactic polypropylene. Combination of dimethyl titanocene and its Cp-substituted analogues and TiCl3 for propylene polymerizations has been reported in U.S. Pat. No. 2,992,212 and by G. A. Lock in xe2x80x9cThermoplastic Elastomers Based on Block Copolymers of Ethylene and Propylenexe2x80x9d, Advances in Polyolefins (Seymour, Raymond B., ed.) at pages 59-74. MAO was not used in this polymerization.
Typically catalysts for traditional polymerization of olefin monomer include a Ziegler-Natta-type polymerization catalyst component, a co-catalyst which is generally an organoaluminum compound, and an external electron donor or selectivity control agent, often an organosilicon compound. Such catalysts are described in U.S. Pat. No. 4,107,413; 4,294,721; 4,439, 40; 4,115,319; 4,220,554; 4,460,701; and 4,562,173.
U.S. Pat. No. Pat. 4,530,914 discloses use of a catalyst system comprising two or more metallocenes in the polymerization of xcex1-olefins, primarily ethylene, to obtain broad molecular weight distribution. Such metallocenes each have different propagation and termination rate constants and are mixed with an alumoxane to form the catalyst system.
U.S. Pat. No. 4,808,561 discloses reacting a metallocene with an alumoxane and forming the reaction product in the presence of a support; a porous material such as talc, inorganic oxides such as those of Groups IIA, IIIA, IVA, or IVB metal oxides such as silica, alumina, silica-alumina, magnesia, titania, zirconia and mixtures thereof, and resinous materials such as polyolefins, particularly finely divided polyethylene.
The disclosures of these patents are hereby incorporated by reference.
A Ziegler-Natta type polymerization catalyst generally is basically a complex derived from a halide of a transition metal, for example, titanium, chromium or vanadium with a metal alkyl, typically an organoaluminum compound, as a co-catalyst. The catalyst is usually comprised of a titanium halide supported on a magnesium compound complexed with an alkylaluminum co-catalyst.
It is known that two or more homogeneous catalysts, such as those based on metallocene compounds, may be combined to effect properties, such as molecular weight distribution. U.S. Pat. No. 4,530,914 discloses use of a catalyst system comprising two or more metallocenes in the polymerization of xcex1-olefins, primarily ethylene, to obtain a broad molecular weight distribution. The metallocenes each have different propagation and termination rate constants. The metallocenes are mixed with an alumoxane to form the catalyst system. It is also known that metallocenes may be affixed to a support to simulate a heterogeneous catalyst. U.S. Pat. No. 4,808,561 discloses reacting a metallocene with an alumoxane and forming a reaction product in the presence of a support. The support is a porous material like talc, inorganic oxides such as Group IIA, IIIA IVA or IVB metal oxides such as silica, alumina, silica-alumina, magnesia, titania, zirconia and mixtures thereof, and resinous material such as polyolefins, e.g., finely divided polyethylene. The metallocenes and alumoxanes are deposited on the dehydrated support material.
In U.S. Pat. No. 4,701,432 it is taught that a support is treated with at least one metallocene and at least one non-metallocene transition metal compound. To form a catalyst system a cocatalyst comprising an alumoxane and an organometallic compound of Group IA, IIA, IIB and IIIA is added to the supported metallocene/non-metallocene. The support is a porous solid such as talc or inorganic oxides or resinous materials, preferably an inorganic oxide, such as silica, alumina, silica-alumina, magnesia, titania or zirconia, in finely divided form. By depositing the soluble metallocene on the support material it is converted to a heterogeneous supported catalyst. The transition metal compound, such as TiCl4, is contacted with the support material prior to, after, simultaneously with or separately from contacting the metallocene with the support.
It is known that Cp2TiCl2 in the presence of alkylaluminum compounds polymerizes ethylene but not propylene whereas in the presence of methylalumoxane (MAO) Cp2TiCl2 polymerizes propylene also to produce atactic polypropylene. Combination of dimethyl titanocene and its Cp-substituted analogues and TiCl3 for propylene polymerizations has been reported in U.S. Pat. No. 2,992,212 and in xe2x80x9cThermoplastic Elastomers Based on Block Copolymers of Ethylene and Propylenexe2x80x9d, G. A. Lock, Advances in Polyolefins, p. 59-74, Raymond B. Seymour, Ed. MAO was not used in this polymerization.
Use exists for improvement of conventional or traditional Ziegler-Natta catalyst activity without the expense and safety concerns of use of pure metallocene-type catalyst systems. Our invention fills this need and alters polymer properties in polymerization processes by use of a supported Ziegler-Natta catalyst which has been modified by metallocene-type catalyst compound.
Our invention provides means to change polymer properties in polymerization processes using a supported Ziegler-Natta catalyst which has been modified with a metallocene compound.
We further provide means to produce polymerized monomer, particularly polyolefin, having low molecular weight and narrow molecular weight distribution.
Additionally we provide improved catalyst activity by modifiying conventional Ziegler-Natta catalyst, preferably during synthesis.
Such provisions are accomplished by catalyst system comprising a supported conventional Ziegler-Natta catalyst modified with a metallocene compound used in polymerization of monomers, notably olefins, especially ethylene.